Vertical crustal movements in Estonia determined from precise levellings and observations of the level of Lake Peipsi

The aim of this study was to evaluate vertical velocities of the benchmarks and their change over time based on the four precise levellings of the Estonian levelling network from 1933 to 2011, with the mean epochs being 1936.7, 1961.2, 1982.1 and 2006.9. The vertical velocities of the benchmarks were estimated using two mathematical models. Both models gave similar results for almost all levelling combinations. Significant discrepancies between the velocities from two models were found only in two combinations where levelling loops’ closing time was long compared to the time between the mean epochs of levellings. From the analysis of post-adjustment variances of unit weight and the ANOVA test, a significant change in the benchmark velocities between mean epochs of the levellings was detected. However, due to correlation between the second and third levellings it remained unresolved whether the velocity change was a real change or fortuitous when relying only on this correlation. The detected velocity change could also be explained by the levelling error. Iterated variance component estimation assigned most of the error to the first levelling. In addition, level records of Lake Peipsi from 1921 to 2006 were used for the first time to calculate lake tilt between water gauges. Velocities of the benchmarks from the combination of the last three levellings and water gauges of Lake Peipsi were used to compile the map of the vertical crustal movements (EST2015LU). The main feature of the compiled map was the SE–NW directional postglacial land uplift. However, compared to earlier maps for the region, our isolines declined more in the W–E direction, due to the larger influence of the fourth levelling and velocities from lake tilts. Overall fit of the compiled map with the velocities of continuously operating Global Navigation Satellite System reference stations and coastal tide gauges was ± 0.4 to ± 0.5 mm yr–1.